The major aim of this project will be to test the hypothesis that the cardiovascular adaptations associated with increased levels of habitual physical activity in a sample of older adults will produce improvements in major quantifiable parameters, cognitive functioning, mood, and psychosocial functioning that have been previously noted to decline with advancing age. One hundred twenty old (60-69 years) healthy volunteers of both sexes will be randomly assigned either to a high intensity supervised aerobic exercise program (65-80% max VO-2), to a low intensity exercise program (less than 35% max VO-2) or to a no-exercise biweekly lecture series control group. At entry and after the completion of six months of exercise (or lecture series) subjects will undergo physiological and psychological testing. Cardiovascular function will be assessed by fatigue-limited exercise testing with expired gas analysis. Cognitive function will be assessed by two reaction time experiments that will examine potential changes in both the efficiency and attentional demands of short-term and long-term memory. In addition, subjects will complete a battery of neuropsychological tests, psychometric tests, and a semi-structured psychosocial interview. All subjects will also undergo a third follow-up assessment six months after the formal completion of the structured exercise program. We hypothesize that the cardiovascular adaptations associated with high intensity physical exercise training will be associated with significant improvements in cognitive abilities and psychosocial functioning. These improvements are expected to be greater than those observed for the low intensity exercise group, who will receive an equivalent amount of social stimulation but not cardiovascular conditioning. Data generated from this study will have important practical significance by determining the extent to which an intervention can improve the physical and psychological well-being of the elderly. The data will also have scientific significance through its potential to expand basic knowledge regarding (a) the cardiovascular physiology and cognitive functioning of normative aging, and (b) the extent to which the psychological and cardiovascular declines typically observed in normal aging may be modified through a program of aerobic conditioning.